U analysis reveals how the
brain works

By Diane SwanbrowNews and Information Services

A
new analysis of the human brain at work, published in the March 12 issue
of Science, elucidates how the frontal lobes are organized,
providing strong evidence that verbal and spatial memories are processed
in different hemispheres.

The analysis, by U-M psychologists Edward E.
Smith and John Jonides, focuses on working memory, a mental system that
includes the temporary storage of verbal, spatial and object information,
and various "executive processes" for using that information. Among the
processes are everyday mental activities such as paying attention to one
source of information but not another as a way of dealing with conflicting
information.

"How the frontal cortex is organized is a question of
tremendous interest," says Smith, the Arthur W. Melton Collegiate
Professor of Psychology and a research scientist at both the Mental Health
Research Institute and the Institute for Social Research. "Our analysis
suggests that it is partly organized by the type of information being
processed and partly by the type of operation being performed--either
storage or active manipulation of the stored information."

Verbal
storage tasks activate left-hemisphere speech areas, Smith and Jonides
found, while spatial storage tasks activate specific areas of the right
cortex. Storage of information about objects, such as smiling vs frowning
faces, activates still different, more ventral, or lower, regions at the
front of the cortex.

Smith and Jonides also found that two of the
fundamental executive processes--paying attention to one source of
information rather than another, and switching from one task to
another--activate specific regions at the front of the brain--the anterior
cingulate and the dorsolateral prefrontal cortex.

Their analysis is
based on brain imaging experiments, done at the U-M and elsewhere, using
PET (positron emission tomography) and functional MRI (magnetic resonance
imaging) scans. The images were made while subjects were actively engaged
in a variety of mental tasks, including an experimental task designed to
isolate a specific memory process and a control task that differed from
the experimental task only in that it did not involve the memory
process.

Long thought to be the seat of higher mental functions such as
planning and problem-solving, the frontal cortex comprises one-third of
the human brain, a proportion much larger than in other primates, Smith
notes.

"Damage to the prefrontal cortex is common in accident victims,"
he says. "They have trouble concentrating on some things while ignoring
others or switching from one task to another. These are the kinds of
activities involved in the executive functions that we're studying."

In
accident or stroke victims with damage to specific regions of the frontal
lobes, a more precise understanding of how various regions of the frontal
cortex are involved in specific mental activities should allow health care
professionals to devise more effective compensatory therapies, according
to Smith. "If you know that an area involved in processing short-term
memory for spatial information has been damaged," he says, "you can work
on developing more elaborate verbal presentations of the information, to
help people process the same information using a different
modality."

Major funding for the study was provided by the U.S. Office
of Naval Research, the National Institute on Aging, and the McDonnell-Pew
Program in Cognitive Neuroscience.